1. Field of the Invention
The present invention relates generally to end blocks for batteries and more particularly to an end block construction which eliminates components, reducing cost while maintaining structural integrity. In its most preferred form, the present invention relates to end blocks for zinc/bromine or other flowing electrolyte batteries, which include recesses for the terminal electrodes, as well as a simplified support structure designed for structural rigidity.
2. Description of the Prior Art
In U.S. Pat. No. 5,002,841, owned by the assignee of the present invention, a conventional flowing electrolyte bipolar battery is shown. It includes a stack of cells, an electrolyte pump, an electrolyte reservoir, a cooling element, and external studs in electrical communication with the terminal electrodes. Each cell is comprised of an electrode upon which the anodic reaction takes place and an electrode upon which the cathodic reaction takes place.
In typical bipolar batteries, each electrode comprises two poles, such that the anodic reaction occurs on one side of the electrode and the cathodic reaction occurs on the opposite side of the same electrode. In contrast to monopolar batteries which require two separate electrodes per cell, a bipolar battery consists of only one structure. As with a monopolar battery, the cells in a bipolar battery are electrically connected in series. Unlike a monopolar battery, however, where the cells are hydraulically isolated, the cells of a flowing electrolyte bipolar battery are hydraulically connected in parallel. The '841 patent describes current flow and the structure of bipolar batteries of the zinc/bromine type and is incorporated herein by this reference.
One of the requirements for flowing electrolyte bipolar batteries are end blocks, between which are sandwiched the cells stacks. The end blocks are supporting structures and provide the framework for duct and shunt tunnels to communicate with interiorly disposed elements of the flow system of the battery. Additionally, the blocks support the terminal studs which electrically communicate with the end or terminal electrodes of the cell stack. Not only must the blocks be inert to the various chemicals of the fluid anolyte/catholyte system, the end blocks must resist bending or bowing caused by different pressures which exist between the atmosphere and the internal operating environments of such batteries. In a typical zinc/bromine battery, operating pressures may easily reach 15 psi. Bowing of the end plates may result in non-uniform electrolyte distribution, resulting in a significant reduction in voltage and/or discharge capacity.
In zinc/bromine batteries, bowing of the end block may also result in poor zinc plating, causing undesirable dendritic growth which, if uncontrolled, could provide a short circuit for current in a particular cell and eliminate its voltage contribution.
Various attempts have been made to provide end blocks which minimize bowing and the resulting problems described above. Steel plates coated with inert material have been employed, leading to a sacrifice of an important battery design criteria, i.e. weight. Others have used plastic corrugations on the end plate to provide additional strength, leading to the sacrifice of another battery design criteria, i.e. overall volume. The solution proposed in the aforementioned '841 patent is a lightweight, deflection-resistant end block which included a base member made of a lightweight, chemically inert and chemically resistive material having one or more cavities for housing low density, substantially rigid inserts, such as honeycombed aluminum. The inserts are encapsulated by a cover welded or otherwise secured to walls located on the base member. The base member also extends beyond the walls to provide a means for receiving the various ducts carrying the flowing electrolyte to and from the interior of the battery, thereby isolating the inserts from possible exposure to the electrolytes. While the foregoing design represented a significant improvement over prior designs, four components are required (including the two insets), each of which has to be manufactured to relatively close tolerances and which require care in assembly.
In addition to the end block structures, such as those disclosed in the '841 patent, batteries of this type typically include a frame on the inside of each end block, such frames having compartments for receiving the terminal electrodes. The frames are additional elements required to construct the battery, and the elimination of such components would result in a desirable savings in the number of components required. The combined elimination of components from the end block and from the structure used to house the terminal electrodes would represent a significant advance in this art.